PAGs

Question 1

culturing microorganisms in a lab

Answer 1

1) Using a sterile petri dish containing agar jelly
2) microorganisms are transferred to the plate from a sample(bacteria in a broth) using a sterile implement(wire inoculation loop)
3) incubate plates adding nutrients to the agar to help improve growing conditions of the microorganisms

Question 2

aseptic techniques

Answer 2

Aseptic techniques prevents contamination of cultures by unwanted microorganisms which may affect growth of microorganisms being cultured / give imprecise results / hazardous to health / costly(industrial scale)

1) long hair tied back
2) work near bunsen burner - hot air rises + convection currents
3) regular disinfection of surfaces
4) sterilisation of instruments before + after use via bunsen burner
5) neck of broth past flame before + closing - air moves out of container
6) minimise the time which the agar plate is open + seal lid immediately - reduces chances of airborne contamination of culture + inoculation cabinet(chamber which contains sterile air)
7) sterilse all glassware before + after use on an autclave(machine whch steams equipment at high pressure)

Question 3

factors affecting the growth of microorganisms

Answer 3

1) using sterile pipette, add same volume(o.1cm3) of sample bacteria from broth to each of 6 agar plates then discard pipettes safely after use
2) spread broth across entire surface of agar using a wire inoculation loop(sterilise)
3) put lids on agar plates + tape them shut
4) 3 plates = fridge at 4’
3 plates = incubator at 25’
incubate upside down to stop condensation forming on the lid from dropping the agar
5) negative controls = same but without bacteria
6) leave plates for 24hrs + count number of colonies formed + record results + work out mean number of colonies per temperature

pH = buffers
nutrient availability = different preparations of agar
use of spectrophotometer = turbity(cloudiness) of broth(high = more cells present = more replication taken place)